From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: Determining if an ext4 fs uses the whole partition
Date: Mon, 30 Apr 2012 13:26:04 -0500
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To: Daniel Drake <dsd@laptop.org>
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On 4/30/12 1:18 PM, Daniel Drake wrote:

...

> Trying the statfs approach (the fs in question is already mounted):
> 
> # dumpe2fs -h /dev/mmcblk0p2 | grep "Block count\|Block size"
> dumpe2fs 1.42 (29-Nov-2011)
> Block count:              949248
> Block size:               4096
> 
> # stat -f /
>   File: "/"
>     ID: f09a7645207bdd68 Namelen: 255     Type: ext2/ext3
> Block size: 4096       Fundamental block size: 4096
> Blocks: Total: 934935     Free: 198205     Available: 188947
> Inodes: Total: 227824     Free: 133103
> 
> The numbers don't agree.
> 
> (Not a big deal, since I can use the other 2 approaches you mentioned,
> just wanted to point it out)

Oh, that's because statfs on extN subtracts out the "overhead" from superblocks,
block group descriptors, etc.    I guess that's a reasonable interpretation
of "/* total data blocks in file system */" but honestly I forgot that
it did that... TBH, not entirely sure why it does.

-Eric